ZF says change the "lifetime ATF" every 8 years or 100,000 miles; BMW used to include ATF as part of their service interval, I think at 60,000 miles; "Bimmer" magazine's old school maintenance schedule confirms the 60,000 mile interval; now that I'm set up to do ATF in an afternoon, I'm going to do a 30,000 mile (every two years) interval, or 50,000 mile if I'm lazy!